Computer cooling system and method of use

ABSTRACT

A reliable, leak-tolerant liquid cooling system with a backup air-cooling system for computers is provided. The system may use a vacuum pump and a liquid pump and/or an air compressor in combination to provide negative fluid pressure so that liquid does not leak out of the system near electrical components. Alternatively, the system can use a single vacuum pump and a valve assembly to circulate coolant. The system distributes flow and pressure with a series of pressure regulating valves so that an array of computers can be serviced by a single cooling system. The system provides both air and liquid cooling so that if the liquid cooling system does not provide adequate cooling, the air cooling system will be automatically activated. The heat may be removed from the building efficiently with a cooling tower.

1.0 CLAIM OF PRIORITY

The present application claims priority as a non-provisional of Ser. No.61/595,989 filed on Feb. 7, 2012. The present application claimspriority as a non-provisional of Ser. No. 61/451,214 filed on Mar. 10,2011. The present application further claims priority as a continuationin part to Ser. No. 13/308,208 filed on Nov. 30, 2011 which is anon-provisional of Ser. No. 61/422,564 filed on Dec. 13, 2010. Thepresent application further claims priority as a continuation-in-part toSer. No. 12/762,898 filed on Apr. 19, 2010. The full disclosure of eachof these references is herein incorporated by reference.

2.0 TECHNICAL FIELD

The present invention relates to systems and methods for coolingcomputer systems.

3.0 BACKGROUND

Arrays of electronic computers, such as are found in data centers,generate a great deal of heat. An example Central Processing Unit of acomputer (“CPU”) generates over 100 watts of heat and has a maximum casetemperature of about 60 C. An example rack of 88 CPUs may generate 9 kWof heat. The outdoor temperature at a hot urban location might be 45 C,so even in hot environments heat can still theoretically flow away fromthe higher temperature computer and toward the lower temperature outsideenvironment. Accordingly, no refrigeration of computers should berequired, theoretically. Nonetheless, the standard way to keep datacenters cool is to use expensive and relatively inefficientvapor-compression refrigeration systems at least part of the time. Theseconventional cooling or “air conditioning” systems often use more powerthat the computers themselves, all of which is discharged to theenvironment as waste heat. These systems use air as the heat transfermedium, and it is due to the low heat capacity and low thermalconductivity of air that refrigeration must be used to remove the heatgenerated by multiple air heat exchangers. Removing heat generated byheat exchangers is also referred to as overcoming the thermal resistanceof the heat exchangers. Some operators use evaporation of cooling liquidto cool cooling liquid-to-air heat exchangers that cool computers, andthis is more thermally efficient than refrigeration, but the computersrun hotter, reducing their reliability, decreasing their efficiency andmaking the data center uncomfortable for human occupants. Water is usedas the cooling liquid or coolant throughout this disclosure, but it willbe known to those in art that other coolants may be used. The coolingliquid may consist essentially of water, including tap water, or maycomprise one or more perfluorocarbons or avionics cooling liquids. Thecooling liquid may flow over a plated surface.

Water has approximately 4000 times more heat capacity than air of thesame volume, so water is a theoretically ideal heat transfer agent fordirect heat transfer from heat generating components. Other coolingliquids offer similar performance. Liquid cooling is recognized as athermally efficient way to cool computer CPUs due to their highconcentration of power and heat generation in a small space, but therest of a computer's electronics generate heat at a lower rate andtemperature, so air-cooling is appropriate for much of the associatedhardware. Current systems may use liquid cooling to move the heat fromthe CPU to a radiator mounted close to the CPU, or they may use anair-to-liquid heat exchanger to remove heat from the computer enclosureand heat-up liquid in the heat exchangers. These systems suffer from thehigh thermal resistance and bulkiness of air-to-liquid or liquid-to-airheat exchangers. Other systems use a chilled cooling liquid loop to coolthe computer, but these systems require complex and expensive connectorsand plumbing to connect the server to the building cooling liquid supplywhile insuring that no leaks occur, which may be devastating in or neara computer. Accordingly, operators of server systems are rightlyconcerned about leaks and reliability of cooling liquid-cooledcomputers. Furthermore, chillers require a large amount of power.Additionally, for operation in a data center, servers, particularlyblade servers, need to be compact. Therefore, what is needed is acompact cooling solution adaptable for up to a large number ofcomputers, that combines and balances air-cooling capacity forlow-intensity heat sources with cooling liquid-cooling capacity forhigh-intensity heat sources while using a minimum amount of coolingliquid flow, and that is reliable, leak-free and low in powerconsumption.

4.0 SUMMARY

The present system addresses these issues and more by providing invarious example embodiments an efficient and compact heat exchanger fora CPU utilizing liquid under negative pressure to minimize chances ofleakage, with an air-cooling backup system. Also provided is a coolingsolution that integrates with an air-cooled heat sink for backup andutilizes only the minimum amount of water necessary to provide adequatecooling for each heat-generating element. Various embodiments furtherprovide systems and methods to cool the CPU, the server and the datacenter with liquid in an optimal manner, by cooling the CPU to reduceleakage current, removing heat from the data center by means of the aircooled portion of the CPU heat exchanger, and utilizing an outdoorevaporative cooling system or dry cooler with part time evaporativecooling system that eliminates the need for a chiller in the liquidcooling system. Additionally, provided is a system and method fordisconnecting and reconnecting liquid-cooled heat exchangers withoutlosing any water. Heat exchangers employing efficiency-increasingturbulators are also provided.

Provided in various embodiments is a system for cooling one or moreelectrical devices inside a building, comprising: one or more liquidcoolant-containing heat exchangers thermally coupled to one or moreelectrical devices and each having a liquid input port and a liquidoutput port and containing liquid coolant at below atmospheric pressure;a liquid coolant-containing chamber in fluid communication with theliquid output port of the heat exchanger(s), the chamber containingliquid coolant and gas at a pressure at least as low as the pressure ofthe liquid coolant in the heat exchanger(s); a vacuum pump in vacuumcommunication with the gas in the chamber; a fluid pump with a fluidintake port in fluid communication with the liquid coolant in thechamber and a fluid output port in fluid communication with liquidcoolant in an evaporative cooler operating at substantially atmosphericpressure and located at least partially outside the building; theevaporative cooler in fluid communication with the liquid input port ofthe heat exchanger(s); wherein the fluid pump in combination with thevacuum pump cause the liquid coolant to flow from the chamber throughthe evaporative cooler and the heat exchanger(s) and back to thechamber. Alternatively, the optional evaporative cooler or otherexternal cooling means can be in a separate loop not in fluidcommunication with the electronics-mounted heat exchanger system, whichmay transfer heat to the external cooling loop via an additionalwater-to-water (liquid-to-liquid) or other heat exchanger.

Also provided in various embodiments is a system for cooling at leastone electrical device inside a building, comprising: one or more liquidcoolant-containing heat exchangers thermally coupled to a firstelectrical device and having a liquid input port and a liquid outputport and containing liquid coolant at below atmospheric pressure; asystem of first and second chambers comprising: a first liquidcoolant-containing chamber in one-way fluid communication with theliquid output port of the heat exchanger, the first chamber containingliquid coolant and gas; a second liquid coolant-containing chamber inone-way fluid communication with the liquid output port of the heatexchanger, the second chamber containing liquid coolant and gas; avacuum pump switchably in vacuum communication with the gas in the firstand second chambers; an a source of higher pressure air switchably inpressure communication with the gas in the first and second chambers;the liquid coolant in the first and second chambers in one-way fluidcommunication with liquid coolant in an evaporative cooler operating atsubstantially atmospheric pressure and located at least partiallyoutside the building; the evaporative cooler in fluid communication withthe liquid input port of the heat exchanger; wherein the vacuum pump andthe higher pressure air source coordinates with the system to seriallypressurize and depressurize the first and second chambers and therebycause the liquid coolant to flow substantially steadily from heatexchanger through the system of first and second chambers to theevaporative cooler and back to the heat exchanger. Once again, theoptional evaporative cooler or other external cooling means can be in aseparate loop not in fluid communication with the electronics-mountedheat exchanger system, which may transfer heat to the external coolingloop via an additional water-to-water or other heat exchanger.

In any of the systems the liquid coolant-containing heat exchangers maycomprise one or more turbulators, and may also be thermally coupled tothe atmosphere adjacent the electrical device, where a fan may urgecirculation of the atmosphere adjacent the liquid coolant-containingheat exchangers. A vacuum accumulator may be in fluid communication withand between the evaporative cooler and the heat exchangers. Theturbulator may be located in a heat exchanger tube and configured toforce the liquid coolant to flow in a path having a length more thantwice the largest dimension of the heat exchanger tube, or may beconfigured to reduce the cross-sectional area of the flow path of theliquid coolant to less than 50% of the cross-sectional area of the heatexchanger tube. The turbulator may define a conical helix flow path forthe liquid coolant, may direct a jet of liquid coolant against a surfaceproximate one of the electrical devices, may define a rectangularcross-section helical liquid coolant flow path, a round cross-sectionhelical liquid coolant flow path, a rectangular cross-sectionsingle-entry helical liquid coolant flow path, a rectangularcross-section double-entry helical liquid coolant flow path, a roundcross-section single-entry helical liquid coolant flow path, a roundcross-section single-entry helical liquid coolant flow path, or a roundcross-section double-entry helical liquid coolant flow path. It may alsodefine a helical path in which the direction of the helix reversesperiodically, for example from left handed to right handed. For purposesof this aspect of the disclosure a square cross-section is considered aspecial case of a rectangular cross-section, i.e., one where the sidesare the same length. Systems are provided wherein a portion of theliquid coolant flows axially over the outer surface of the turbulator,thereby causing swirl and turbulence in the flow path and increasing theheat transfer effectiveness of the turbulator.

Also provided are systems comprising: a connector releasably connectingthe liquid coolant-containing heat exchanger to the chamber, theconnector adapted to release the liquid coolant-containing heatexchanger from the chamber only when substantially all of the liquidcoolant has been evacuated out of the heat exchanger. For example,provided is a supply valve in removable fluid communication with theliquid input port of the heat exchanger; a return valve in removablefluid communication with the liquid output port of the heat exchanger;wherein the supply valve is actuatable to open the liquid input port ofthe heat exchanger to atmospheric pressure air that is at a higherpressure than the water inside the heat exchanger and thereby evacuatethe water from inside the heat exchanger; the supply valve and returnvalve being constructed to close and disconnect the heat exchanger fromthe system after the water is evacuated from inside the heat exchanger.A passive latching system is also provided. The latching system mayinclude a mechanical delay in order to prevent premature disconnection.

Provided in various systems is a liquid level sensor located in thechamber and providing an output based on the level of the liquid in thechamber, the fluid pump being adapted to operate in response to theoutput of the fluid level sensor. In other embodiments, provided arefluid level sensors located in both the first and second chambers andproviding first and second outputs, respectively, based on therespective levels of the liquid in the chambers, the vacuum pump and thepressure pump each being adapted to operate in response to one or bothof the first and second outputs and to maintain the fluid levels in thechambers within predetermined ranges.

Systems may further comprise a vacuum regulator in vacuum communicationwith the vacuum pump and adapted to maintain a pressure in at least aportion of the system less than atmospheric pressure. Also provided maybe a filter in fluid communication with the liquid coolant-containingheat exchanger and adapted to prevent debris from entering the liquidcoolant-containing heat exchanger or valves. Additionally provided is apressure regulator in fluid communication with the liquidcoolant-containing heat exchanger, the pressure regulator adapted toprovide a constant pressure differential across the liquidcoolant-containing heat exchanger. A dome loaded, spring biasedregulator, as is known in the art may accomplish this.

A method is provided of modifying a non-liquid cooled electrical deviceheat exchanger with fins extending from a base to become liquid cooled,comprising the steps of: removing at least a portion of one or more ofthe fins and thereby making accessible a portion of the base; andaffixing liquid cooling tubing having an input port and an output portto at least a portion of the exposed base.

A method is also provided of disconnecting a heat exchanger from asystem for cooling at least one electrical device, as described hereinwhere the system comprises: providing such a system, and actuating thesupply valve and opening the liquid input port of the heat exchanger toatmospheric pressure air that is at a higher pressure than the coolingliquid inside the heat exchanger; evacuating the cooling liquid frominside the heat exchanger; closing the supply valve and the returnvalve; and disconnecting the heat exchanger from the system after thecooling liquid is evacuated from inside the heat exchanger. This methodmay also apply to systems with a plurality of heat exchangers.

Further provided is a method of minimizing the energy needed to coolheat-generating electronics inside a cabinet having a higher thanambient temperature, comprising the steps of: providing a heat exchangercomprising: a thermally conductive base adapted to thermally couple tothe heat-generating electronics; a plurality of thermally conductivefins extending outward from the base; and one or more cooling liquidpathways thermally coupled to the base and the fins; balancing thethermal load of the heat generating electronics and the ambient airinside the cabinet by positioning the one or more cooling liquidpathways relative to the base and the fins; thermally coupling the heatexchanger to the heat generating electronics; and providing a source ofcooling liquid to the one or more cooling liquid pathways. This methodmay also comprise the steps of: providing a fan and locating the fan sothat it causes air to flow across one or more of the fins; and balancingthe thermal load of the heat generating electronics and the ambient airinside the cabinet by: positioning the one or more cooling liquidpathways relative to the base and the fins in further view of the heattransfer effect of the fan; and adjusting the speed of the fan.

Also provided is a system that uses one vacuum pump to circulate coolantunder negative pressure. The system includes a pump connected to avacuum line such that the pump creates a pressure of less thanatmospheric on the vacuum line. The vacuum line, along with apressurized line, is connected to a valve assembly, and that assembly isconnected to a first and second fluid chamber. A coolant circuit isprovided that allows coolant to circulate through the first and secondchambers, through a primary heat exchanger and through an electricaldevice heat exchanger. The circulation is accomplished through acontroller that operates the valve assembly. The circuit may also have areservoir, various pressure and temperature sensors, and other valvesand nozzles to optimize the system. The controller operates the valveassembly by substantially alternating between (a) actuating the valveassembly to create a higher pressure in the first coolant chamberrelative to the second coolant chamber, thus emptying coolant from thefirst coolant chamber and drawing coolant into the second coolantchamber; and (b) actuating the valve assembly to create a higherpressure in the second coolant chamber relative to the first coolantchamber, thus emptying coolant from the second coolant chamber anddrawing coolant into the first coolant chamber. The system may alsooptionally have a coolant recovery devices so as to minimize themaintenance of the system.

Other aspects of the invention are disclosed herein as discussed in thefollowing Drawings and Detailed Description.

5.0 BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingfigures. The components within the figures are not necessarily to scale,emphasis instead being placed on clearly illustrating example aspects ofthe invention. In the figures, like reference numerals designatecorresponding parts throughout the different views and/or embodiments.It will be understood that certain components and details may not appearin the figures to assist in more clearly describing the invention.

FIG. 1 is a diagram of a vacuum-pumped liquid cooling system accordingto various example embodiments.

FIG. 2 is a top plan view of an example air and cooling liquid-cooledheat exchanger incorporating a turbulator.

FIG. 3A is a partial section view of the example air and coolingliquid-cooled heat exchanger with turbulator of FIG. 2.

FIG. 3B is a partial section view of the example air and coolingliquid-cooled heat exchanger with turbulator of FIG. 2.

FIG. 4 is a perspective view of the example turbulator of FIGS. 2, 3Aand 3B.

FIG. 5 is a diagram showing an example cooling liquid clearingdisconnect system in normal operation.

FIG. 6 is a diagram showing the example cooling liquid clearingdisconnect system of FIG. 5 during the disconnect process.

FIG. 7 is a diagram showing the example cooling liquid clearingdisconnect system of FIG. 5 in a disconnected state.

FIG. 8 is a diagram of a vacuum-pumped liquid cooling system accordingto various example embodiments.

FIG. 8A is a diagram of a vacuum-pumped liquid cooling system accordingto various example embodiments.

FIG. 8B is a diagram of a vacuum-pumped liquid cooling system accordingto various example embodiments.

FIG. 9A is a section view of a vacuum accumulator used to prevent dropsof cooling liquid from leaving the system when it is disconnected, shownin a low-vacuum condition.

FIG. 9B is a section view of the vacuum accumulator of FIG. 9A, shown ina high-vacuum condition.

FIG. 10 is a perspective view of a turbulator assembly comprising asingle-entry flow passage turbulator having a rectangular cross-sectionand positioned inside a flow channel, partially cut-away.

FIG. 10A is a top plan view of the turbulator of FIG. 10.

FIG. 10B is a side elevation view of the turbulator of FIG. 10.

FIG. 10C is a top plan view of a turbulator with a rectangularcross-section and a double-entry flow passage.

FIG. 10D is a top plan view of a turbulator with a circularcross-section and a single-entry flow passage.

FIG. 10E is a perspective view of a turbulator with a circularcross-section and a double-entry flow passage.

FIG. 10F illustrates a cross-sectional views of a turbulator.

FIG. 10G illustrates a cross-sectional views of a turbulator.

FIG. 10H illustrates a turbulator traveling through a heat exchanger.

FIG. 10I illustrate a turbulator traveling through a heat exchanger.

FIG. 11 is a perspective exploded view of an example air and coolingliquid cooled heat exchanger with turbulators positioned near theprimary heat source.

FIG. 12 is a perspective view of an example air heat exchangerretrofitted to become an air and cooling liquid cooled heat exchanger.

FIG. 13 is a side elevation view of an example air and cooling liquidcooled heat exchanger with a turbulator positioned further from theprimary heat source.

FIG. 14 is a perspective view of an example air and cooling liquidcooled heat exchanger with turbulators positioned in the fins.

FIG. 15 is a diagram showing heat flow relationships in an exampleserver environment that uses a liquid and air cooled heat exchanger.

FIG. 16 is a section view of a side elevation of a valve according tovarious example embodiments.

FIG. 17A is a heat flow diagram depicting the heat flow in an examplesystem using only air cooling.

FIG. 17B is a heat flow diagram depicting the heat flow in an examplesystem using liquid cooling and air cooling.

FIG. 18 is a diagram of a vacuum-pumped liquid cooling system accordingto various example embodiments.

FIG. 19A is a section view of a side elevation of an example valve in anexample cooling liquid clearing disconnect system in normal operation.

FIG. 19B is a section view of a side elevation of an example valve inthe example cooling liquid clearing disconnect system of FIG. 19A duringthe disconnect process.

FIG. 19C is a section view of a side elevation of an example valve inthe example cooling liquid clearing disconnect system of FIG. 19A in adisconnected state.

FIG. 20 is a chart of temperature data resulting from tests of examplecomputer cooling systems according to various example embodiments.

FIG. 21 is a chart of power consumption data resulting from tests ofexample computer cooling systems according to various exampleembodiments.

FIG. 22 is a schematic of a single vacuum pump cooling system accordingto an example embodiment.

FIG. 23A is a top view of a of a single vacuum pump cooling systemaccording to an example embodiment.

FIG. 23B is an isometric view of a of a single vacuum pump coolingsystem according to an example embodiment.

FIG. 24 is a schematic and top view of a single vacuum pump coolingsystem according to an example embodiment when the main chamber isemptying.

FIG. 25 is a schematic and top view of a single vacuum pump coolingsystem according to an example embodiment when the auxiliary chamber isemptying.

FIG. 26 is a schematic of a single vacuum pump and coolant recoverysystem according to an example embodiment.

FIG. 27A is a schematic of a valve that may be used on the coolantsupply side according to an example embodiment.

FIG. 27B is a schematic of a valve that may be used on the coolantreturn side according to an example embodiment.

6.0 DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Following is a non-limiting written description of example embodimentsillustrating various aspects of the invention. These examples areprovided to enable a person of ordinary skill in the art to practice thefull scope of the invention without having to engage in an undue amountof experimentation. As will be apparent to persons skilled in the art,further modifications and adaptations can be made without departing fromthe spirit and scope of the invention, which is limited only by theclaims.

6.1 Example Negative Pressure System Designs

Referring to the example liquid cooling system 100 shown in FIG. 1, thesystem 100 provides liquid cooling under negative pressure for an arrayof computers or other heat generating devices with liquid heatexchangers 1 with a minimal flow rate and a minimal volume of coolingliquid in order to provide cooling in an efficient and reliable manner.The system 100 may be the same as that disclosed in U.S. Pat. Pub. No.2011/0253347 A1 to Harrington, published Oct. 20, 2011, the fulldisclosure of which is incorporated herein by reference. In certainembodiments the system 100 includes a cooling tower 11, which may beoutdoors, to cool the cooling liquid 12, a cooling liquid distributionsystem 4, 5 to supply cooling liquid to multiple CPUs, high performanceheat exchangers 1 to remove heat from said CPUs with a minimum flow rateand pressure drop, a vacuum pump 8 to suck cooling liquid 12 throughsaid CPUs heat exchangers and to remove any excess air that may enterthe system 100. Water can be used for the cooling liquid 12 due to itslow viscosity and high heat capacity. Alternatively, perfluorocarbons,avionics cooling liquids or any other suitable fluids may be used. Inaddition the system 100 may include an air-cooled heat exchanger (see,e.g., air-cooled heat exchanger 21 in FIG. 2) attached to each CPU toremove the heat in the event that the liquid cooling system 100 is notoperating. The fan that is typically connected with a CPU heat exchanger(not shown) may also be used to cool the interior of the computer bytransferring heat from the air inside the computer to the cooling liquidso that other components within the server enclosure may be cooled withor without the use of external air flow. An air-to-liquid heat exchangermay also be used to remove any excess heat from the portions of theserver not cooled by the liquid cooled heat exchanger.

In the example embodiment shown in FIG. 1, a supply of cooling liquid 12is maintained at a low temperature by the evaporation of the coolingliquid as it flows out of nozzle 13. The humid air flows out due to fan14 in cooling tower 11. Due to the low pressure in the chamber 6, thecooling liquid flows through a filter 9, and check valve 18 and a supplypipe 5, through a pressure regulator 3, through another check valve 16with a cracking pressure of approximately 1 in Hg, through a vacuumaccumulator 17 and then through a fluid connector 2, to the computer,server, or server rack with internal heat exchanger 1. The coolingliquid 12 then receives heat from the internal electronic components inthe computer, such as the CPU, and flows out through the connector to anextraction pipe 4 and then to the chamber 6. A vacuum is maintainedwithin the chamber 6 by the vacuum pump 8. The vacuum pump 8 could be apiston type with a Teflon or similar seal, which has a long lifetime, orit could be a linear pump or a diaphragm pump or any other suitablepump. A liquid ring pump is particularly suitable for this application,in that it pumps moist air well. The vacuum pump 8 may be compatiblewith the humidity and any chemical used to prevent corrosion or biofilmgrowth. A float valve 51 may be used to keep cooling liquid 12 out ofthe inlet of the vacuum pump 8, as shown with respect to vacuum pump 53in FIG. 8. The vacuum pump 8 may be controlled by a pressure sensor 15to maintain an absolute pressure that is above the vapor pressure of thecooling liquid 12 in its heated state, to keep the cooling liquid 12 inits liquid phase. The chamber 6 may include a level sensor 7 andregulator such that if a certain level is exceeded, the liquid pump 10speeds up, thereby pumping cooling liquid 12 out of the chamber 6 andinto the cooling tower 11. This may provide a constant pressuredifferential to multiple heat sources 1. The cooling tower 11 willrequire makeup cooling liquid to replace cooling liquid that isevaporated, as is known in the art of evaporative coolers generally. Theoptional cooling tower 11 to cool down the cooling liquid 12 may useconvection and evaporation in order to reduce the temperature of thecooling liquid 12 to the local wet bulb temperature or whatevertemperature is required by the CPUs, which is typically less than 30 C.

The cooled cooling liquid 12 is preferably moved through the heatexchanger 1 under a pressure that is less than the local atmosphericpressure. In certain embodiments the entire system 100 runs at a lowabsolute pressure, so that any leaks are of air into the system 100,rather than cooling liquid 12 out of the system 100. One potential issuewith cooling liquid-cooled negative pressure systems is that at lowabsolute pressures, cooling liquid may boil. For example, at 50 C, waterboils at 4 in Hg absolute, so the pressure in water-based systems cannotget that low. Accordingly, this limits the potential pressure dropavailable to each heat exchanger 1 to the difference between the vaporpressure of the warmest cooling liquid 12 within the system 100 and thelocal absolute atmospheric pressures. Maximum pressure drops availablefor each heat exchanger 1 are thus substantially less than oneatmosphere. The remainder of the available pressure drop must be usedfor plumbing to and from the heat exchangers 1 and the pump 10,including head loss, elevation changes, and increases in flow resistancedue to fouling.

The plumbing 4, 5, etc. to and from the computer/server/CPU heatexchangers 1 may be designed for unusually low pressure drop, so as tokeep the total pressure drop of the system 100 within the aforesaidlimits. This may be accomplished in certain embodiments by using, forexample, simple surgical tubing or similar light-duty material withlarge-radius bends and low-pressure-drop fittings, which would not workwith conventional high-pressure systems. Conventional high-pressuresystems typically use heavier-duty plumbing with sharp bends and largepressure-drop interfaces, which combine to create systems having toomuch overall pressure drop to work as described herein.

Alternatively, the plumbing 5, etc. to the computer/server/CPU heatexchangers may be high pressure plumbing supplied by an additional pump(not shown), with a pressure regulator 3 to reduce the pressure to belowatmospheric as the cooling liquid 12 gets close to the electronics. Forthe return plumbing 4, etc., larger pipes may be required for the flowof air and cooling liquid, as air will be introduced to the system ascomputers/servers are removed or replaced. Local air removal systems(not shown) may be used in order to prevent the return plumbing 4, etc.,from getting too large. Such systems may use local vacuum pumps,plumbing to a central vacuum pump, or float actuated drain valves andmultiple compartments, as in U.S. Pat. No. 4,967,832 to Porter,published Nov. 6, 1990, the full disclosure of which is incorporatedherein by reference.

Each server or computer with a liquid heat exchanger 1 may have an inletpressure regulator 3 and an outlet pressure regulator (not shown) inorder to maintain a desired pressure drop across the CPU heat exchanger1. Each CPU may have a temperature sensor (not shown), and an increasein temperature over the inlet cooling liquid temperature may indicate aproblem with the heat exchanger 1. A temperature sensor, such as athermistor, may be used to measure the inlet cooling liquid temperature.Flow meters, such as a rotameter, thermal mass flow sensor or turbinemeter with a digital readout (not shown), may also be used to monitorthe flow. The filter 9 may be used after the cooling tower 11 and beforethe heat exchanger 1 to prevent clogging of the passages in the heatexchanger 1. Chemical additives may be used to prevent fouling of theheat exchanger 1 with biological films and to prevent corrosion. Theinternal passages of the heat exchanger 1 may be plated or anodized toprevent corrosion.

The cooling liquid chamber 6 is preferably at lower pressure than theheat exchanger on the device being cooled 1. This can be accomplished bykeeping the chamber 6 at a lower elevation than the heat exchanger 1 orby means of a check valve with a given cracking pressure or a pressureregulator (see, e.g., check valves 38 and 49 in FIG. 8). This willprovide negative pressure at the CPU heat exchanger 1 by means ofgravity head. Example cooling liquid distribution systems 100 mayprovide the cooling liquid 12 at a pressure of approximately −2 in Hg tothe computer/server/CPU heat exchangers 1. This may be accomplished bymeans of the design of the system 100, or by placing apressure-regulating valve 3 at the server or rack level. The plumbingfrom the fluid supply chamber 6 to the computer/server/CPU heatexchangers 1 may require an additional pump (not shown) in the feed line5 if the computer/server/CPU heat exchanger 1 is at a significantlyhigher elevation than the cooling tower 11, such as if it is on a higherfloor than the cooling tower 11. Such a supply pump's speed may becontrolled so that the pressure at the computer/server/CPU heatexchangers 1 is at the correct value.

For the fluid pump 10, a seal-less centrifugal pump with a magneticdrive may be used, as well as a solenoid pump with an internal fluidiccheck valve, such as described in U.S. Pat. No. 1,329,559 to Tesla,published on Feb. 3, 1920, the full disclosure of which is incorporatedherein by reference. In addition, a system may be required to prime thepump 10, as is known in the art of pumps. For example, this may beaccomplished by turning off the liquid pump 10 and allowing fluid 12 toflow back through the pump 10. A flow actuated shuttle valve in the pumpoutput (not shown) may be at a default off position allowing the vacuumpump to suck fluid into the chamber 6. Once the liquid pump 10 is primedand the level sensor 7 activated, the liquid pump 10 may then turn onand pump the fluid out of the chamber 6 and into the cooling tower 11. Apump 10 with low net positive suction head (NPSH) is preferred, so thatthe cooling liquid does not cavitate at the inlet of the pump 10. Thefluid pumps 10 and vacuum pumps 8 for the system 100 may be selected tobe reliable and have a long life. They also may provide a steadypressure on the suction side, and a low pressure on the outlet, in orderto deliver flow to the cooling tower 11. One example design for maximumoperational life would be to use a dual chamber pump such as describedin, for instance, U.S. Pat. No. 7,611,333 B1 to Harrington, published onNov. 3, 2009, the full disclosure of which is incorporated herein byreference, due to the very low NPSH required and due to its ability toreject bubbles from the inlet flow. Such a pump, when driven by a vacuumpump and an air compressor, may provide a very low inlet pressure and anindependent output pressure. This type of pump may be fitted withadditional backup vacuum pumps and compressors (not shown) connectedwith check valves so that any single point failure would not cause asystem-wide failure. In addition, the check valves and pressurizationand vacuum valves and controls may include redundant units (not shown).A condenser and automatic drain system may be required to capture anycoolant vapor and droplets which may be pumped out by said vacuum pump.

Although a computer or server or server rack with a liquid heatexchanger 1 is described, systems such as system 100 maybe used to coolany electronic component. Although water is described in variousembodiments, any coolant 12 may be used instead of or in addition towater. Although the system 100 is described as using cooling liquid 12for evaporation and for cooling, a liquid-to-liquid heat exchanger maybe used to transfer heat from an evaporator 11 to a closed system (notshown) so that any coolant 12 may be used to interact with the hotcomponents such as CPUs, such as a non-corrosive or non-conductivecoolant. This may be used in the case of evaporative coolers 11 that usesalt water or reclaimed water, for example. In this way, the coolantused for the computer heat exchangers 1 may be separate from the coolingused for other systems. Then the heat can be transferred from one systemto another using, for instance, a plate type heat exchanger in aseparate cooling loop. For low temperature operation, as in Northernlatitudes, a radiator (not shown), fan 14 and glycol system may be usedto reject the heat while preventing freezing of the coolant 12. A mistersystem can evaporatively pre-cool the air going into the radiators (drycoolers) for use during occasional hot days. Since CPUs can get up to 60C, cooling liquid 12 can be heated to 50 C and still be used to cool theCPUs. The cooling liquid used for cooling the computers may be kept at atemperature higher than the dew point of the air in the data center toprevent condensation on the plumbing or the heat exchangers.

Referring now to the example liquid cooling system 800 shown in FIG. 8A,the centrifugal pump 8 and chamber 6 of FIG. 1 has been replaced by amultiple chamber pump which acts as a vacuum pump, chamber, coolingliquid/air separator and pressure pump. In example liquid cooling system800, the system may use a plurality of chambers, such as a main chamber6 and an auxiliary chamber 56. The operation of example system 800 is asfollows: the cooling liquid 12 flows under suction in to the chamber 6from the extraction pipe 4 through check valve 49. The pressure in thechamber 6 is maintained at a low level by vacuum pump 8, which isconnected to the chamber by valve 44. A vacuum chamber, 55 may be usedto provide a steadier suction. A vacuum chamber 55 may likewise belocated at each server rack 1, and it may have a float actuated waterrelease to allow for the release of any accumulation of water. Suchlocal air release systems may require local vacuum pumps 8 or connectionto a central vacuum system (not shown).

The cooling liquid flows into the chamber 6 until the level sensor 41indicates that the chamber 6 is nearly full. Then the valve 34 opens,connecting the vacuum pump 8 with the auxiliary chamber 56 and loweringthe pressure of auxiliary chamber 56 so that cooling liquid may flowinto it from the extraction pipe 4 through check valve 38. Once flow ofcooling liquid is established into both chambers 6 and 56, valve 44shuts and valve 43 opens, connecting chamber 6 with the pressure pump 53and thereby pressurizing main chamber 6 so that cooling liquid flowsthrough check valve 48 and into the cooling tower 11. Then the level inchamber 6 reaches a low level, as indicated from level sensor 42, atwhich time the valve 43 shuts. Then the valve 44 opens and flow is againestablished under suction into the main chamber 6, at which time theauxiliary chamber vacuum valve 34 is shut and the valve 33 is openedconnecting chamber 56 with the pressure pump 53 and forcing coolingliquid out of chamber 56 through check valve 39 until the level in thechamber 56 reaches the low level sensor 32. Under normal operation levelsensor 31 would not be activated because the system is designed so thatthe flow out of the chambers 6, 56 is higher than the flow into thechambers 6, 56, so that the auxiliary chamber 56 is never completelyfull, thereby allowing for the flow through the heat exchangers 1 to besteady while the flow to the cooling tower 11 is intermittent.Accordingly, the level sensor 31 can be used to indicate if there is asystem failure. The pressure and vacuum levels can be monitored by thepressure pump 53 and the vacuum pump 8 using the pressure sensors 54 and15. The entire system can be controlled by a computer or by a logiccircuit or any other suitable means. Floats 51 may be used to sense thelevels in the chambers 6, 56 and reduce evaporation of the coolingliquid 12 in the chambers 6, 56.

Referring to FIG. 8B, the system 800′ may be substantially the same asthe system 800 in FIG. 8A, except the system 800′ may further include atest valve 61 and a purge valve 62 and a pressure sensor (not shown).Test valve 61 and purge valve 62 and the pressure sensor may be used totest the system 800′ for leaks and to purge air out of the system 800′.Temperature sensors (not shown) may also be added to the plumbing atlocations 4 and 5 to provide data for determining the flow rate of heatremoved by the system 800′. The duration of time that the vacuum pump 8is on can be used to determine the rate of air flow in the system 800′and thereby the presence of an air leak can be inferred, for instancewhen the vacuum pump 8 runs longer or more often than normal. Thepressure at the vacuum pump inlet may also be used to determine theamount of air flowing through the system, or an air flow sensor may beused. The operator can be alerted if excessive air is finding its wayinto the system. The entire pumping and monitoring system 800′ canoutput data in real time to populate a web page or other output (notshown) that displays various parameters regarding the system in realtime, such as, for example, heat pumped, air leak rate, coolantresistivity, pH or TDS, and the like. The pressure and level in the pumpchambers can also be reported. The current to the air pump 53 and vacuumpump 8 can be measured and monitored to determine if either one ismalfunctioning or wearing out. The plumbing 4, 5 from the pump system tothe racks of computers/servers with liquid heat exchangers 1 can beconnected with quick connect fittings such as, for instance, thoseavailable from the John Guest Corp., so that racks and servers 1 may beeasily reconfigured.

Referring to FIG. 18, a system 1800 may be provided incorporating any orall of the features from systems 100, 800, or 800′, except system 1800demonstrates the option of using a closed and/or sealed liquid pumpingsystem 800″ to re-circulate liquid through liquid-cooledcomputers/servers/server racks 1 without exposing that liquid to theopen atmosphere (and resulting contaminants) of an external coolingsource such as a cooling tower 11. This may be accomplished by, forinstance, providing a liquid-to-liquid heat exchanger 1890 thattransfers heat from the liquid used in the liquid-cooledcomputers/servers/server racks 1 to a separate liquid 12 that is cooledexternally, for instance by a cooling tower 11, as shown in FIG. 18. Inthe example embodiment shown in FIG. 18, cooled liquid 12 pumped fromthe cooling tower 11 enters the exchanger 1890 at a first cooledposition 1891, and travels through the exchanger 1890 while picking upheat from the hot liquid leaving the computers 1 until that now-heatedliquid 12 exits the exchanger 1890 at a second heated position 1892,after which it returns to the cooling tower 11 to be cooled. At the sametime, separate heated liquid leaving the computers 1 enters theexchanger 1890 at a first heated position 1893, and travels through theexchanger 1890 while dissipating, losing, or otherwise transferring heatto the cool liquid from the cooling tower 11 until that now-cooledliquid exits the exchanger 1890 at a second cooled position 1894, afterwhich it returns to the pumping system 800″, having never mixed with theliquid 12 that flows through cooling tower 11. Systems such as system1800 may advantageously use a clean, controlled liquid to circulatethrough the computers 1, while using a less expensive liquid such asgray water or sea water in the cooling tower, which needs to besupplemented regularly to make up for evaporation losses.

Also shown in system 1800 is a flow sensor 1830. The flow sensor 1830may include a self heated thermistor or RTD, such that if the liquidcoolant stops flowing, or the coolant is too hot, the fan 1840 is turnedon to high speed. This could be accomplished by flowing a known currentthrough a thermistor such that in still coolant, and under 25 C ambientconditions, the thermistor temperature rose to 35 C. A comparatorcircuit could detect the voltage decrease associated with thetemperature rise and a MOSFET could be switched on to control the speedof the fan 1840. Under air cooling conditions the power to fan 1840would typically be on all the time, but under liquid-cooled conditions,the power to the fan 1840 could be pulse width modulated at 10-500 Hz toslow down the fan 1840 but not allow it to stop. The controller for thefan 1840 is represented by unit 1850. These features are applicable toany of the present systems.

Referring to FIGS. 9A and 9B, an example vacuum accumulator 17 is shownin cross-section, having a liquid inlet 61 and liquid outlet 63. Thevacuum accumulator 17 comprises a flexible diaphragm 62 which may beflat or nearly flat in state 900 when no pressure differential existsbetween inside and outside the accumulator 17, as in FIG. 9A. When avacuum or pressure less than the external atmosphere is provided by thesystem inside accumulator 17 as in state 900′, the flexible diaphragm 62is displaced inward toward the liquid and holds a steady position asshown in FIG. 9B. If the CPU heat exchanger 1 is disconnected from therest of the system 100, 800, 800′, 1800, etc., then the check valve 16shuts and the diaphragm 62 springs back into the flat position 900 as inFIG. 9A. This tends to suck cooling liquid toward the accumulator 17 andaway from fluid connector 2, prevent dripping of liquid out of thesystems 100, 800, 800′, 1800, etc.

Any leakage in the system may be detected by monitoring the cycle timeof a pump 8 used to remove air from the systems 100, 800, 800′, 1800,etc. If the pump 8 is cycling on too often, then a leak is indicated.The leak may be discovered by pulling a vacuum on each heat exchanger 1and measuring the decrease in vacuum over time. A simple hand operatedvacuum pump may be used for this type of testing.

Systems 100, 800, 800′, 1800, etc. may use a pump with a chamber (notshown) to supply fluid to all the heat exchangers 1. During a shutdownprocedure, the pump may evacuate the system; purge it with air and storethe fluid until such time as the liquid cooling system is reactivated.During a reactivation procedure, the pump control system may apply avacuum or a pressure to the system, check to see if the fluid systemloses vacuum or pressure and then start pumping again, based on the rateof change of the system pressure.

6.2 Example Dry-Disconnect Systems

FIG. 5 provides a diagram of an example coolant clearing system innormal operation 500, depicting the cooling liquid flowing through asupply valve 71 and then through a heat exchanger, 21, and then outthrough a return valve 72, all at less than atmospheric pressure. Inthis configuration the valves 71, 72 are both open to flow of coolingliquid and are sealed from the higher-pressure outside air.

FIG. 6 shows a diagram of the cooling liquid clearing system of FIG. 5during the disconnect process 600. Before disconnecting the fluid supplyand extraction lines (not shown), the valve 71 is opened to outside air,which allows higher-pressure outside air to flow into the valve 71 andinto heat exchanger 21, shown schematically. The valve 71 may beconnected to a latch (not shown) that prevents the fluid lines frombeing removed until the valve 71 is depressed or otherwise actuated toallow entry of air. The latch can be configured to remain in a latchedposition, so valve 71 remains actuated to allow entry of air until theconnector (not shown) is reinserted into the computer.

FIG. 7 shows a diagram of the cooling liquid clearing system of FIG. 5upon completion of the disconnect process 700, when the heat exchanger21 is disconnected from the liquid cooling system 100. Upon completionof the disconnect process 700, the supply valve 71 is unactuated to sealthe valve 71 from outside air so that air does not flow into the coolingsystem 100. And return valve 72 is likewise unactuated to seal the valve72 from outside air so that air does not flow into the cooling system100. Return valve 72 may be unactuated by a pin or latch (not shown) sothat it shuts off when the heat exchanger 21 is disconnected from theliquid cooling system 100. The connector may be designed to prevent thedisconnection of the heat exchanger 21 from the liquid cooling system100 until all the liquid is removed from the heat exchanger 21. Such adisconnection prevention feature could be activated by the change insubatmospheric pressure present in the suction in the return line as thereturn line changes from being filled with cooling liquid to beingfilled with air. For example, the pressure drop across the heatexchanger 21 would be less as the heat exchanger 21 changes from beingfilled with cooling liquid to being filled with air. This change inpressure drop could be calibrated to trigger the connector to allowdisconnection of the heat exchanger 21 from the liquid cooling system100 when the heat exchanger 21 changes from being filled with coolingliquid to being filled with air. This draining process may be helped bythe following connector arrangement. To detach the connector in oneembodiment, the operator depresses a button (not shown) that operates athree-way valve 71 that cuts off inlet cooling liquid flow and vents toallow air into the system 100. Negative pressure on the return side ofthe connector holds the connector in until air reaches the outlet. Atthis point, the negative pressure in the system is diminished due to themuch lower delta pressure of air flowing through the heat exchanger andthen the connector may be easily removed. Removal of the connector sealsthe outlet so that air does not continue to flow into the cooling systemreturn flow path. The button stays depressed, thereby sealing off theinlet. To attach the connector, the operator would insert the coupling,which would connect the return path, and the button would automaticallyrelease, which would allow the supply flow to reach the components 1.This system may also be actuated with a twist instead of a button push,or by any other means of activation. Example connectors adaptable foruse with the present system are described in U.S. Pat. No. 7,602,609 B2to Spearing et al., published as application US 2008/0298019 A1 on Dec.4, 2008, the full disclosure of which is incorporated herein byreference. The connector may utilize a sacrificial metal, such as zincor utilize electrical potential to prevent corrosion inside the CPU heatexchanger 1. Using tap water that has a slight alkaline content for thecooling liquid 12 may reduce the corrosion rate for copper and brassheat exchangers 1.

For example, the computers/servers with liquid heat exchangers 1 may beconnected to the pumping system using a connector 1600 such as shown inFIG. 16, which prevents the user from disconnecting the server until theserver is purged of cooling liquid. This connector 1600 may be used inconjunction with vacuum pumping systems 100, 800, 800′, etc. Theconnector design 1600 in FIG. 16 achieves this in a two-step process.First, the user or another mechanism depresses the button 1610 whichcloses off the supply line 1620 to the server 1 and allows air to flowin through port 1640 into the system 100, 800, 800′, etc. At that pointthe top spool valve 1650 will have moved downward (toward the bottom ofthe page in FIG. 16) but the bottom spool valve 1660 will not have movedyet, because its movement will be resisted by a hydraulic lock createdby liquid still present in the bottom chamber 1670 below the spool valve1660, which liquid will take a short period of time to be sucked out.The leak rate from bottom chamber 1670 is selected such that the secondspool valve 1660 does not move until enough time has passed to ensurethat the server 1 is purged of liquid 12. Thus, the spool valve is amechanical device that creates a delay in releasing the connection,during which time the fluid can be evacuated avoiding a leak.

Then, once the fluid 12 is evacuated from the bottom chamber 1670 to apredetermined level, a larger leak opens up, the bottom spool valve 1660drops all the way to the bottom of bottom chamber 1670, and the valve1600 is closed or sealed from both the supply 1620 and return 1630lines. The valve 1600 may be latched in the closed position until it isreconnected to a server 1, at which point both spools 1650, 1660 riseand the supply and return lines 1620, 1630 flow freely and the bottomchamber 1670 is refilled. The valve 160 may also be held in theintermediate position (i.e., with top spool valve 1650 closed whilebottom spool valve 1660 remains open) by the negative pressure whichwill be present until the server 1 is purged of liquid 12. For example,a spring loaded diaphragm or piston (not shown) could hold the valve inthe intermediate position until the negative pressure was reduced, as itwould be once the server 1 was completely vented of liquid. The valve1600 may also be triggered by pressure differences created with anorifice or venturi, which differences would be higher when flowingliquid than when flowing gas, as is known in the art of fluid mechanics.

FIGS. 19A, 19B and 19C illustrate an example connector valve 1901 asdiscussed above, further comprising an example latching system 1905,1915. The valve 1901 is shown in operation in a latched open position1900, in a latched intermediate position 1900′, and in a closedunlatched position 1900″. Such a connector 1901 will allow air to enterthe computer/server with liquid cooling 1910 through a port 1920 as thevalve 1901 is pushed down into the intermediate position 1900′. If theserver 1910 has a minimum volume of cooling liquid 12, the server 1910may be purged of cooling liquid 12 in less than one second while in theintermediate position 1900′. Once the cooling liquid 12 is purged fromthe server 1910, it is also purged from the bottom chamber 1940 belowthe lower valve 1930. Once the cooling liquid 12 is purged from thebottom chamber 1940 below the lower valve 1930, the lower valve 1930moves to the bottom of the bottom chamber 1940 and the valve 1901 movesto the closed position 1900″, thereby closing the air port 1920 as wellas the plumbing 4, 5 for the cooling liquid 12. The movement of thelower valve 1930 to the bottom of the lower chamber 1940 also movesdownward a connected latching mechanism 1905 that thereby disengages acorresponding latching mechanism 1915 that is connected with the server1910. The disengagement of latching mechanisms 1905, 1915 allows theconnector valve 1901 and plumbing 4, 5 connected thereto to be removedfrom the server 1910 without leakage of cooling liquid 12, for instanceif component repair or replacement is required. A small amount of airmay be pulled into the system during this process, but it will beautomatically evacuated and pumped out by the vacuum pump(s), e.g.,vacuum pump 8.

Each computer or server or server rack with a liquid heat exchanger 1may be connected with the present dry disconnect system that allows forthe automatic draining of the heat exchanger 1 as described above. Suchconnectors may include supply and return flows. Supply and return flowsmay be coaxial, in order to allow for a small interconnect. The systemis preferably designed to remove all of the cooling liquid from insideeach heat exchanger subsystem 1 such as a CPU, server or server rackduring the disconnection process. For example, if the heat exchanger 1contains one cc of cooling liquid 12, and the flow rate is 150 cc/minuteof cooling liquid, then it will take less than 1 second to drain thecooling liquid out of the computer or server or server rack with aliquid heat exchanger 1. As the cooling liquid 12 is replaced by air,the flow resistance of the heat exchanger decreases, so the process mayhappen in less than 0.5 seconds.

6.3 Example Turbulator Designs

Referring to FIG. 2, an example air and cooling liquid heat exchanger200 may comprise a cooling liquid cooling portion 210, which includesinlet tube 22 and outlet tube 23 to provide cooling liquid (not shown)to a turbulator 400 (shown in more detail in FIGS. 3A, 3B and 4, its topsurface 20 being visible in FIG. 2), and a metal heat spreader 24 thatis in thermal contact with the electronic device 1820 (shown in FIG. 18)on one side and is in thermal contact with the cooling liquid on theother side. A series of fins 21 are provided in thermal contact withflowing air in the event that the liquid cooling system is notoperational. A fan 1840 (shown in FIG. 18) would typically be used inproximity to the fins 21 to provide cooling air. A turbulator 400 fitsinside the metal heat spreader 24 and reduces the amount of coolingliquid needed to cool the device and increases the velocity andturbulence level in the cooling liquid. In this example air and coolingliquid heat exchanger 200, the cooling liquid inlet 22 may be adapted toprovide a point of jet impingement cooling closest to the heat source,for instance near surface 20, as best seen in FIGS. 2, 3A, 3B and 4, toflow the cooling liquid in a helical path 25 through the turbulator 400to the outlet tube 23. In some cases a portion of the cooling liquidflow may flow over the helical flow passages 25 through a clearancespace between the turbulator 400 and the metal heat spreader 24 as bestshown in section view 300. This “leakage” of cooling liquid flow overthe edges of helical flow passages 25 may enhance heat transfer bycausing turbulence and swirl within the helical flow passages 25.

FIG. 3A shows a partial cross-sectional side elevation view 300 of theair and liquid heat exchanger 200 shown from the top in FIG. 2. Theturbulator 400 can be seen installed in FIG. 3B in the heat spreader 24,and providing a narrow helical path or passage 25 for the coolingliquid. The CPU is not shown in this view; it would normally be attachedto the bottom or lower portion of the heat spreader 24 as shown incross-sectional side elevation view 300. In other embodiments the CPU orother heat source could be located proximate the upper portion of theheat spreader 24, for instance near surface 20. FIG. 4 provides anisometric view of the turbulator 400, which shows the helical flow path25 more clearly.

With reference to FIG. 11, a liquid-cooled heat exchanger 1100 ispreferably mounted to a CPU (1820, shown in FIG. 18) and may compriseone or more passages 1130 with turbulators 1001 to increase the velocityand turbulence of the cooling liquid 12 near the heat transfer surface1111. The turbulator 1001 may also be designed to minimize the volume ofcooling liquid 12 contained within the heat exchanger 1100 so that thecooling liquid 12 may be quickly cleared for repairs. The CPU 1820typically includes an air-cooled heat exchanger with fins 1810 and a fan1840 located nearby to provide air-cooling. The fan 1840 may becontrolled by the temperature of the CPU 1820 so that as it gets hotter,the fan speed increases. The flow rate of the cooling liquid 12 may bedetermined by the acceptable temperature rise of the liquid and thepower dissipated by the CPU 1820. For an example CPU that generates 100watts, a stream of cooling liquid at 150 cc/minute may result in atemperature rise of approximately 10 C. The temperature differentialfrom the CPU case to the cooling liquid should be of the same order asthe temperature rise. The heat exchanger 1100 in that example may beselected to have a pressure drop of approximately 4 in Hg so that thesystem 100 will work properly on a hot day in a high altitude location,where the difference between the local atmospheric pressure and thevapor pressure of the hot cooling liquid may be only about 8 in Hg.

The heat exchanger 1 may incorporate a helical flow pattern for thecooling liquid 12 to put a long path into a short passage to increaseheat transfer. This helical flow passage may have multiple starts andpaths, as shown in FIG. 10E, so as to allow for increased flow in asmall passage. This may also be accomplished by placing a threaded rod,such as shown in FIG. 10D, in a metal tube so that the flow must take along path through the heat exchanger at a high velocity. This has theadded benefit of reducing the volume of cooling liquid in the heatexchanger 1, thereby reducing the amount of cooling liquid 12 that needsto be cleared to service the heat exchanger 1. Alternatively, a rod witha tortuous path in relief may be used to displace fluid in the centerpart of the passage and thereby increase the cooling liquid flow andturbulence, as shown in FIG. 10.

The rod and cylinder may be square, cylindrical, conical, triangular,hexagonal, or any other appropriate shape. The rod or other turbulatorstructure may be designed so that some of the cooling liquid 12 flowsover the edge 1004 of flow passages 1005 in an axial direction, forinstance directly from a proximal end 1002 to a distal end 1003 of theturbulator 1001 shown in FIG. 10A. This axial flow may interact with thehelical flow in channels 1005, 1006 to provide swirl or turbulence inthe heat transfer passages in order to increase heat transfer. This isshown in FIG. 10G and discussed further below. In addition, the axialflow will reduce the flow resistance/pressure drop of the heat exchanger1. This arrangement may be particularly useful in situations where theflow of cooling liquid 12 would otherwise be laminar or nearly laminar.In some installations, a flat plate heat exchanger may be used. For highpower dissipation systems, or for additional reliability, multipleparallel turbulators may be used.

For example, referring to the embodiment shown in FIGS. 10, 10A and 10B,a turbulator system 1000 may include a turbulator 1001 with ridges 1004and troughs 1005 defining a flow passage between the turbulator 1001 andthe interior of a hollow body or tube 1010, for instance a helical flowpassage, that forces cooling liquid 12 flowing from a first end 1002 toa second end 1003 of the turbulator 1001 to flow diagonally across oneface 1020 of the interior of the hollow body 1010, and then across tothe other side 1030 of said passage, where the flow goes diagonallyacross and then back to the previous side 1020, and then repeats thishelical flow pattern from a proximal end 1040 of the hollow body 1010 toa distal end 1050 of the hollow body 1010. The flow passage may be fedwith a fitting 1060, which may include a hose barb. The flow passage maylikewise be drained with a fitting 1070, which may include a hose barb.

Referring to the example embodiment shown in FIG. 10C, an alternateturbulator 1001′ forms a double-entry helical flow path. Thisrectangular cross-section design allow for more flow at a given pressurethan the rectangular cross-section design in FIGS. 10, 10A and 10B, inthat it defines two parallel flow paths. The use of two paths, insteadof one larger path, increases the velocity of the fluid and tends tomake the device resistant to clogging. Also, the dual path reduces thetendency of the flow to short circuit over the top of ridges 1004, thusmaintaining the flow in thermal contact with the heat exchange tube 1010and increasing cooling efficiency.

In the example embodiment shown in FIG. 10D, a circular cross-sectionturbulator 1001″ is provided for use inside of a corresponding circularcross-section tube (not shown). This may be easily constructed incertain embodiments by placing a threaded rod 1001″ in a tube with aclose tolerance. This type of design lends itself to use in some of theembodiment described below, in which the liquid flow path is embedded inthe fins of a heat exchanger in order to reduce the thermal resistanceto the air.

FIG. 10E illustrates yet another type of turbulator 1001′″ with acircular cross-section. Like the rectangular cross-section embodimentshown in FIG. 10C, the circular cross-section turbulator 1001′″ in FIG.10E forms a double-entry helical flow path. To illustrate these paths,FIG. 10E has lighter shading 1005 that illustrates one flow path, anddarker shading 1006 illustrating the independent second flow path. Thisdesign provides more flow at a given pressure than the design in FIGS.10, 10A and 10B, in that it uses two parallel flow paths. The use of twopaths, instead of one larger path, increases the velocity of the fluidand tends to make the device resistant to clogging. Also, the dual pathand circular cross-section reduces the tendency of the flow to shortcircuit over the top of ridges 1004, thus maintaining the flow inthermal contact with the heat exchange tube 1010 and increasing coolingefficiency.

The design of turbulators shown in FIGS. 10A, 10B, 10C, and 10E all havea core that is concentric to the passageway in which the turbualtor isinstalled. Radiating away from the core are fins or ridges that createthe channels in which the coolant flows. FIG. 10F illustrates across-section that is perpendicular to the longitudinal axis of theturbulator 1001″″, while FIG. 10G illustrates a cross-section that isparallel to the longitudinal axis of the turbulator 1001″″. Theturbulator core is labeled 1070 and the fins/ridges 1072. The coreeffectively reduces the cross sectional area of the passageway andforces the coolant through the turbulator at a higher pressure. Whilethis obstruction of the turbulator causes a increase in pressure drop,it has the benefit of causing the coolant to flow in a highly turbulentfashion which increases the heat exchange with the coolant. The crosssectional area of the core relative to the passageway may be greaterthan 20%, but more preferably at least 40 percent. Further, theturbulator may be designed such that the fins/ridges intentionally allowflow or leakage from one channel to an adjacent channel. While at firstblush this may seem to reduce efficiency, it actually causes the coolantto experience even more turbulence by creating swirls that areperpendicular to the flow in the helical channel which increases theheat transfer to the coolant. FIG. 10 H illustrates a turbulator 1001″″traveling through a heat sink 1074, with FIG. 10I showing an enlargedview of the turbulator 1001″″. The turbulator 1001″″ has helicalchannels 1075 (shaded dark gray) and 1076 (shaded light gray) that areadjacent to each other. Because ridge 1078 is designed to allow leakage,a swirl 1080 is created that is substantially perpendicular to thehelical channel flow shown by arrow 1082. The central core of theturbulator may consist of baffles which reduce the flow velocity insteadof solid material. This achieves the goal of increased heat transfer,but it adds unnecessary fluid to the system.

6.4 Example Heat Sink Designs

Referring to FIGS. 11 and 18, in the embodiment shown in FIG. 11 heatexchanger tubes 1010 are soldered into slots 1130 in the base plate 1110of the heat sink 1100, thereby reducing the thermal resistance from theCPU 1820 (located adjacent surface 1111) to the liquid. The turbulators1001 enhance the heat transfer from the liquid 12 to the base of theheat sink 1111 and to the top of the CPU 1820.

Referring to FIG. 12, a fluid supply fitting 1210, heat exchanger tube1010 and fluid return fitting 1230 are added to the heat sink 1200 sothat the cooling system can be connected to a fluid cooling systemwithout affecting the mechanical attachment of the heat sink 1200 to theCPU 1820 or circuit board. The path of the heat exchange tube(s) 1010 isshown by dashed line 1220. Heat sink 1200 can be created from anexisting non-liquid heat sink without changing the footprint of the heatsink by removing a few fins 120 and adding one or more heat exchangertubes 1010 with fluid connections 1210, 1230.

Referring to FIG. 13, in this example embodiment the heat exchanger tube1320 is positioned on the top surface 1330 of the base plate 1110 of theheat sink 1300. In this configuration, the thermal resistance from theCPU 1820 (located adjacent to surface 1111) to the liquid coolant 12(running through tube 1310) is greater than in the design shown in FIG.11. At the same time, the thermal resistance from the liquid to the airin heat sink 1300 is reduced compared to heat sink 1100.

Turning to FIG. 14, in heat sink 1400 the heat exchanger tubes 1420,1440 are placed in the fins 1120, still further away from the base plate1110 than in heat sink 1300. This further increases the thermalresistance from the CPU 1820 (located adjacent to surface 1111) to theliquid coolant 12 (running through tubes 1420, 1430, 1440 and 1450), andfurther reduces the thermal resistance from the liquid coolant to theair. The various example heat sink designs 1100, 1200, 1300 and 1400demonstrate that the distance from the bottom 1111 of the base plate1110 to the tubes 1010, 1130, 1320, 1420, 1440 may be adjusted in orderto adjust and balance the thermal resistance from the liquid coolant 12to the air (through fins 1120) and from the CPU 1820 (adjacent surface1111) to the liquid coolant 12.

6.5 Design Optimization

A thermodynamic model of these competing thermal resistances is shown inFIG. 15. In model 1500, the relationship of the thermal resistance fromthe CPU to the liquid and the air, and from the air to the liquid, isillustrated. By means of the prior embodiments, the thermal resistancefrom the heat sink 1810 to air, the CPU 1820 to the heat sink 1810, theheat sink 1810 to the liquid 12 and the air to the liquid 12 may beadjusted and optimized to minimize overall total power consumption,including that of the entire data center. For example, increasing thenumber or area of the fins 1120, may decrease the thermal resistancefrom the heat sink 1810 to the air. The thermal resistance from the airto the liquid 12 may be decreased by placing the liquid heat exchangertubes 1420, 1440 closer to the center of the fins 1120. For instance, anexample air cooled heat exchanger may have a thermal resistance of 0.15C/watt. The liquid cooled heat exchanger may have a thermal resistanceof 0.05 C/watt. By adjusting the position of the cooling liquid-cooledheat exchanger within the assembly the thermal resistance from the airto the cooling liquid and the CPU 1820 may be suitably controlled so asto provide optimal cooling for the air in the data center and the CPUchip. In some cases, multiple passages may be used to cool both the finsand the processor. Heat pipes and any other thermal structures may alsobe used to control the flow of heat in connection with the presentsystems, as will be apparent to persons of skill in the art uponreviewing this disclosure.

The fan 1840 that is typically connected to the CPU heat exchanger mayalso be used to cool the interior of the computer by transferring heatfrom the air inside the computer to the cooling liquid 12 so that othercomponents within the server enclosure may be cooled with or without theuse of external air flow—i.e., the computer may be sealed. The speed ofthe fan 1840 may be adjusted to remove additional heat from the airinside the server enclosure of the data center as required to minimizethe overall power consumption of the data center. The overall powerconsumption versus fan speed may be determined based on the powerconsumption of the air conditioning system versus temperature in thedata center and the power consumption of the CPU 1820 versus itstemperature. The CPU 1820 uses additional power depending on thetemperature of the processor due to leakage currents, with the leakagecurrents increasing exponentially with the processor at the highertemperature range. For example, CMOS-based processors use more energy asthe temperature of the processor goes up, due to leakage currents. Also,the air conditioning system of the data center uses additional powerdepending on the temperature of the data center and the building heatremoval requirements. This increase is generally linear; with highertemperatures requiring proportionally higher air conditioning power. Bycontrolling and selecting the optimal speed of the CPU fan 1840, theflow rate of liquid 12 through the heat exchanger 1, and the position ofthe liquid heat exchanger tubes 1010, 1130, 1320, 1420, 1440 in theoverall assembly consisting of a base 1110 and fins 1120, the overallpower required for the data center can be decreased. Examples of theserelative flows of heat between the various components are depicted bythe wavy arrows in FIGS. 17A and 17B, and may be analyzed and optimizedusing an electrical analog as shown in example heat flow diagram 1500 inFIG. 15.

With further reference to FIGS. 17A and 17B, it can be seen that the airconditioning system of the data center would use additional power whenthe computers/servers 1 use air cooling only, rather than air coolingplus liquid coolant that is routed outdoors to cool. This heat loaddifference is represented by the comparison of the larger heat load 1710that must be removed from the air of the data center in system 1700 withthe smaller heat load 1720 that must be removed from the air of the datacenter in system 1700′. The difference is represented by heat load 1730that is removed by the liquid, and is preferably routed outdoors to coolas shown in the foregoing embodiments. The design of a heat sink 1810for a system that uses an internal liquid cooling passage could bedesigned to remove heat from other items in the server, such as harddrives, memory chips, and any other heat-generating electronics, asshown in FIGS. 17A and 17B. In these designs the heat sink 1810 may beselected to be oversized for the CPU 1820, but this will reduce thecooling load on the air conditioning system in the data center bytransferring to the liquid coolant not only heat from the CPU 1820, butalso heat from the other nearby heat-generating electronics.

6.6 Example Test Results

An example heat exchanger design started with an existing air-cooledsystem. In order to provide the best cooling with minimum volume andinput power, a spiral cooling channel with a Reynolds number just abovethe laminar limit was used. This is believed to provide the best coolingwith a reasonably sized channel that can pass contamination.

For example, if a 140 watt CPU is to be cooled with water, and an 18degrees F. (10 degrees C.) temperature rise can be accepted, then a flowrate of 220 cc/minute would be needed based on the heat capacity andmass flow rate of water. Next, rocket science was employed to develop anozzle cooling system, which in rocket science is done with an array oftubes that cool the nozzle and preheat the fuel on the way to thecombustion chamber. The goal there is to adjust the length and diameterof the parallel tube array to get the optimum cooling for a given flowrate. In the present case, the water outlet temperature and the heatsink temperature are desired to be within 1 degrees C. of each other. Soa fluid path was selected with a Reynolds number slightly higher than2100, so that the flow was turbulent, but the pressure drop was not toohigh. In this example two helical flow passages were used, 0.055 inch(1.4 mm) in diameter. This system was analyzed using empirical heattransfer equations for flow in a tube, modeled using computation flowdynamics (CFD), and tested with a Xeon processor running stresssoftware. The thermal resistance heat sink to water, based on thetemperature of the water into the heat sink, was 0.04 watt/degrees C.with 230 cc/minute flow rate per CPU. A similar heat sink design withcoolant passages in the base is shown in FIG. 11.

The test heat sink worked exactly as modeled, but when the flow wasincreased, it was discovered that it could actually remove heat from theentire system. A stack of three DL380 servers was run at idle powerlevels in an insulated box and the heat sinks were able to remove allthe heat (700 watts) from the computers. In this case the ambient airwas 107 degrees F. (42 degrees C.) and the coolant inlet was at 76degrees F. (22 degrees C.).

Additionally, a test was conducted with a 2 kW rack of servers in anoffice environment at 75 degrees F. (24 degrees C.) ambient. The serverswere either air-cooled or water-cooled using an outdoor miniaturecooling tower with water at 65 degrees F. (18 degrees C.). Thetemperature data is shown in FIG. 20. When the liquid cooling was turnedoff the HVAC system was not able to keep up, so the door was openedslightly to keep the temperature relatively constant. A set of 7 Servers(3×HP Proliant DL380 G4 2×3.4 GHz and 4 Verari 2U 2× Opteron 245)consumed 2 kW using air-cooling while running a processor stress testprogram (2 instances of BurnK7). With liquid cooling, and slowed-downfans, the power was reduced to 1.8 kW with 1 kW of heat extracted usingthe liquid cooling system. In addition, the average processortemperature decreased 25 F (14 C). The hard drives warmed slightly withliquid cooling due to the reduced airflow, but unlike processors, theylast longer at warmer temperatures.

The RAM temperatures were lower with liquid cooling because the RAMchips were located downstream of the heat exchanger. Assuming a typicaldata center power distribution of 56% Servers, 30% HVAC, 5% UPS and 6%other, the total power required for the original air cooled system wouldbe 3.6 kW (Server Power divided by 0.56). Using liquid cooling allows 1kW to bypass the HVAC system and go directly outdoors, saving HVACpower. And this has a multiplying energy savings effect, since it takesmore than 1 kW of energy for an HVAC system to remove 1 kW of heat. Italso saved 10% of the server input power due to lower fan power andbecause the processors required less power at lower temperatures. Theliquid pump and cooling tower fan used only 50 watts. This reduced theoverall power consumption based on typical data center powerdistribution to 2.9 kW, a total power reduction of approximately 20%.The power reduction is diagrammed in FIG. 21. This experiment was doneusing a miniature cooling tower that was only 52% efficient whichlowered the water temperature down to (65 degrees F.) 18 degrees C. in a(50 degrees F.) 11 degrees C. wet bulb environment. A commercial gradecooling tower with 75% efficiency would be able to reduce thetemperature of the cooling water to (59 degrees F.) 15 degrees C.Assuming that the heat removed is proportional to the difference betweenthe ambient and the cooling water inlet, the more efficient coolingtower would boost the heat removal by 50%, leading to a predicted totaloverall power savings of 25%.

Accordingly, the combination of an air cooled heat sink modified forredundant liquid cooling, a negative pressure system to prevent leaks,and a connector that automatically purges the coolant adds up to asystem that offers a path from the current air-cooled technology to theliquid cooled data center of the future, without having to modify thebuilding. The present liquid cooled and air cooled heat sink systemreverses the thermodynamics of traditional systems so that the heat sinkremoves heat from the CPUs and the server interior and the data centerin general in order to reduce the HVAC loads and fan power by a largemargin.

6.7 Single Vacuum Pump Cooling System

In previously described embodiments, a separate vacuum pump andcirculation pump are used to circulate the coolant throughout the systemat negative pressure. The embodiment shown in FIG. 22 contains onevacuum pump that both circulates the coolant and creates the negativepressure. The benefit to a single vacuum pump system is that it is lessprone to failure and it uses less energy to operate.

Turning in detail to FIG. 22, a single vacuum cooling system 2200contains a single vacuum pump that creates a vacuum line 2202 and thesystem further includes a pressurized line 2204, i.e., a line that is athigher pressure than the vacuum line 2202. The vacuum pump illustratedin FIG. 26 and discussed below. The vacuum line 2202 is connected toboth a main chamber 2206 and an auxiliary chamber 2208, with a valve2210 regulating the vacuum line 2202 to the main chamber 2206 and valve2212 regulating the vacuum line 2202 to the auxiliary chamber 2208. Thepressure line 2204 is connected to both a main chamber 2206 and anauxiliary chamber 2208, with a valve 2214 regulating the pressure line2204 to the main chamber 2206 and valve 2216 regulating the pressureline 2216 to the auxiliary chamber 2208. Valves 2210, 2212, 2214 and2216 make up a valve assembly, and that assembly is controlled by thecontroller 2232. As described below with reference to FIGS. 23 and 24,switching the valves 2210, 2212, 2214 and 2216 will cause the coolant tocirculate throughout the system under negative pressure.

In one embodiment, both the main chamber 2206 and the auxiliary chamber2208 are connected to the reservoir 2218, such that the coolant cantravel in one direction from the main/aux chamber to the reservoir, theone direction travel being accomplished by the use of check valves 2220.The reservoir 2218 is where the coolant is drawn from for circulation tothe electronic equipment, shown as servers 2222, and the removal of heatfrom that equipment through the use of an electronic equipment heatexchanger 2223. The reservoir 2218 connects to the primary heatexchanger 2224 (this can be a liquid-liquid exchanger or an air-liquidexchanger) reducing the temperature of the coolant prior to circulatingthe coolant via cold manifold 2226 to the servers 2222, and returningthe heated coolant via hot manifold 2228 back to the main and auxiliarychambers (2206 and 2208). The coolant from the hot manifold 2228 travelsonly in one direction to the main and auxiliary chambers (2206 and2208), the one direction travel being accomplished by the use of checkvalves 2230. The travel of the coolant throughout the system 2200 isalso referred to herein as the coolant circuit.

Alternatively the main chamber 2206 and the auxiliary chamber 2208 canbe connected directly to the primary heat exchanger 2224, completelyobviating the need for the reservoir 2218. The reservoir 2218, however,is helpful is equalizing the negative pressure through the system 2200,such that the flow of coolant is more constant and less pulsating. Alsothe reservoir 2218 allows the system 2200 to hold more coolant,minimizing the possibility that the system 2200 will run dry.

The system 2200 may also have redundant valves and pumps to reduce thechance of shutdown to a negligible level. One such redundancy system mayhave two vacuum pumps running at 50% capacity, such that if one failsthe other ramps up to cover the load. This redundancy also imbues thesystem 2100 with enough vacuum capacity to work with one servercompletely open to air.

The system 2200 may also have several sensors, filters and structures tohelp optimize its performance. For example, the reservoirs 2218 mayinclude level sensor to make certain that there is sufficient coolingliquid in the system to meet the demands of the electronic equipment.Filters may be placed throughout the system to remove debris that couldinterfere with the valves and negatively affect performance. A set oftemperature (2240) and pressure (2242) sensors may be placed on the coolmanifold and a set on the hot manifold to detect the temperature andpressure difference of the coolant. All the information from thesesensors may be feed to the controller 2232. If for example, the systemdetects insufficient coolant, the system may open the fill valve 2234 toadd more coolant and alert the system operator that the coolant levelwas low. If the pressure sensors detect an abnormal pressure drop, thiscould signal that there is a leak in the system and the system wouldalert the operator. Because the system operates under negative pressure,the leak would not expose the computer equipment to the cooling liquid,but rather would introduce air into the system and potentially reducethe efficiency of the system in cooling the computer equipment. Toreduce the ability of a leak to compromise the cooling efficiency of thesystem a novel set of valves and nozzles are used on the hot and coldmanifolds, and discussed in greater detail with reference to FIGS. 27 Aand B. The system 2200 may also have a condensation return line 2250connected to the main or auxiliary chambers, for use in the capture ofcoolant as described in reference to FIG. 26.

Other valves may be used to further optimize the system. For example,test valve 2236 may be used when the system is first turned on. Testvalve 2236 should remain closed until the system detects at the variouspressure sensors that the appropriate amount of negative pressure hasbeen reached and maintained. This prevents the system from beingactivated with leaks present and prevents coolant from circulating tothe electronic equipment under atmospheric or near atmospheric pressure,such that a leak would actually cause coolant to spill. Purge valve 2238may be used to purge the system of coolant when the system is turnedoff. Again, this prevents coolant from remaining in the electronicequipment plumbing under atmospheric or near atmospheric pressure, suchthat a leak would actually cause coolant to spill.

The components of the system 2200 encompassed by the box 2244 may besufficiently small to be installed as a rack mount device in atraditional server tower. Further those components may be placed on atray such that any leaks that may occur in the rack-mounted unit wouldbe captured by the tray and would not impact any of the serverequipment.

FIGS. 23A and B illustrate a top and isometric view of an actualrack-mountable system 2300 that would be encompassed by box 2244. Theprincipal components of the system include the main chamber 2206 and theauxiliary chamber 2208 that are in one-way fluid communication with thereservoir 2218. Valves 2210 and 2212 are connected to the vacuum line.Valves 2214 and 2216 are connected to the pressure line. Theliquid-liquid heat exchanger 224 is connected to the reservoir 2218.Arrows 2246 illustrate the movement of the coolant in and out of therack-mountable system 2300. A tray 2248 may be placed under the system2300 to capture any liquid that might escape, thus preventing damage toany equipment that is in the same server rack as this rack-mountablesystem 2300. The rack-mountable system 2300 could cool up to 10 kW ofservers in up to 10 racks. This would allow the costs of the system tobe spread out the cost over a number of servers. It would be apparentthat the teaching of this disclosure can be used to cool even largerserver farms.

The operation of the system will now be described with reference toFIGS. 24 and 25. In FIG. 24 the main chamber 2206 is emptying into thereservoir 2218 as shown by arrow 2405 while the auxiliary chamber 2208is filling with water returning from the computer equipment as shown byarrow 2410. This circulation is accomplished by opening valve 2114(which is pressurized) and simultaneously opening valve 2212 (which isunder vacuum). This creates a difference in pressure between the mainchamber 2206 and the auxiliary chamber 2208 of about 10 to 15 in Hg,circulating the coolant though the system. Once the main chamber 2206has emptied sufficiently, then it must be filled and the auxiliaryemptied to continue the circulation. This operation is shown in FIG. 25.In FIG. 25 the auxiliary chamber 2208 is emptying into the reservoir2218 as shown by arrow 2505 while the main chamber 2206 is filling withwater returning from the computer equipment as shown by arrow 2510. Thiscirculation is accomplished by opening valve 2216 (which is pressurized)and simultaneously opening valve 2210 (which is under vacuum). Thiscreates a difference in pressure between the main chamber 2206 and theauxiliary chamber 2208 of about 10 to 15 in Hg, circulating the coolantthough the system. The functions illustrated in FIGS. 24 and 25 arealternatively performed creating a circulation of the coolant using asingle vacuum pump. To optimize the system, there may be slight overlapbetween these alternatives, but the majority of time when one chamber isfilling the other is emptying. The control of the valves is accomplishedby way of the controller 2232.

FIG. 26 illustrates the single vacuum pump 2602 used in system 2200. Thepump compressor 2602 may actually include two or more vacuum pumps toprovide redundancy to the system which would reduce the chance ofshutdown to a negligible level. For example having two vacuum pumps 2602sized to run at 50% capacity, would allow one vacuum pump to take theentire load should the other fail. The vacuum pump is connected to thevacuum line 2202 and its exhaust is outputted to the pressurized line2204. The vacuum pump creates the pressure differential that causes thecoolant to circulate through the system 2200. Prior to the vacuum pump2602 a coolant recovery device 2608 may be placed. Here the coolantrecovery device 2608 is an air/water separator, but other coolantrecovery devices include, and are not limited to, mufflers andthermoelectric devices that condense any moisture out of the air. Infact, a thermoelectric device may be used to condense moisture out ofthe atmosphere in order to make up for any coolant loss. As the vacuumline sucks air out of the main and auxiliary chambers, the air will beat or near 100% relative humidity and if that moisture in the air is notcaptured, then the system will require frequent coolant addition. Thiscan then become an annoying maintenance issue. By routing the vacuumline 2202 through the coolant recovery device 2608, moisture can beremoved from the humid air in the vacuum line 2202. That coolant dropsto the bottom of the device 2608. The device 2608 is connected to mainchamber 2206 via the condensation return line 2250, such that when themain chamber 2206 is under vacuum, there is a pressure differential ofabout 10 to 15 in Hg pushing the recovered coolant to the main chamber2206. A check valve 2610 prevents the coolant from traveling in thewrong direction within the condensation return line 2250. Of course apump could also be used to pump the coolant back to the system. Forexample, a piston pump, gear pump or peristaltic pump would be suitable.

After the vacuum pump 2602, a second coolant recovery device 2604 may beplaced. Here the second coolant recovery device 2604 is amuffler/condenser. Although not shown, the pressurized line 2204 may bevented to atmospheric pressure. When vented in this fashion, the system2200 still operates and the pressurized line 2204 would be atatmospheric pressure and would be pressurized as compared to the vacuumline 2202. As the vacuum pump 2602 evacuates the air, it will still havesome humidity, and if that moisture in the air is not captured, then thesystem will require frequent coolant addition. The second coolantrecovery device 2604, condenses the coolant out of the air, allowing thecoolant to collect at the bottom of the device 2604. Here the coolantrecovery device 2604 is a muffler, but other coolant recovery devicesinclude, and are not limited to, air/water separators and thermoelectricdevices that condense any moisture out of the air. In fact, athermoelectric device may be used to condense moisture out of theatmosphere in order to make up for any coolant loss. The device 2606 isconnected to main chamber 2206 via the condensation return line 2250,such that when the main chamber 2206 is under vacuum, there is apressure differential of about 25 to 30 in Hg. A float valve 2606 may beused, such that the valve 2606 is closed until a sufficient amount ofcoolant has collected at the bottom of the device 2604. Once the valve2606 opens, the pressure differential pushes the recovered coolant tothe main chamber 2206. Of course a pump could also be used to pump thecoolant back to the system. For example, a piston pump, gear pump orperistaltic pump would be suitable.

6.8 Flow Control in the Event of a Single Point Gross Leak

In the event that one of the servers has a damaged liquid cooling systemand is leaking air into the system through a completely broken coolantconduit, the rest of the system should still operate provided that theleakage rate into both sides of the liquid cooling system is controlled.

Referring to FIGS. 27A and B, structures that can control the leakagerate are described. FIG. 27A illustrate a valve 2705 on the supply side(i.e., the valve 2705 is upstream of the electronic equipment as definedby the direction of coolant flow shown by arrow 2710) and FIG. 27Billustrates a valve 2715 on the return side (i.e., the valve 2715 isdownstream of the electronic equipment as defined by the direction ofcoolant flow shown by arrow 2720). In one embodiment these valves may beplaced near the hot and cold manifold 2228, 2226) as shown in FIG. 22.On the supply side (valve 2705), the coolant may flow through a checkvalve, such as the one described by Tesla or a fluid diode, or a poppetand seat type of check valve with a built in leak. A groove in the seatcan provide the necessary leak. The opening in the seat is shown at2725, which allows a leak across the valve 2705 shown as arrow 2730. Thereverse flow through the valve 2705 must be such that any coolant in theline upstream from the valve 2705 can be sucked back into the coldmanifold 2226 and not leak out on the electronic equipment 2222. Theleak, however, must not be so severe so as to adversely affect the otherservers in the loop by introducing too much air into the system.

On the return side (valve 2715), the air flow must not be so excessiveas to reduce the pump effectiveness substantially. One way to achievethis goal is to use a Venturi, which has a low pressure drop whenflowing coolant at the nominal flow rate, and limits the flow of airinto the system to that which can flow through the minimum diameter ofthe Venturi at the speed of sound. For example, a Venturi with a throatof 0.05 inches, will have a pressure drop of approximately 1 in Hg at300 cc/min coolant flow rate, and it will flow approximately ½ standardcubic feet per minute of air at 20 in Hg vacuum. A large-scale systemdesigned to cool 100 kW of servers may flow approximately 35 gal/min ofcoolant. A completely open sever line would therefore representapproximately 17% of the overall volume flow rate, and the system couldstill efficiency cool the electronic equipment.

6.9 Leak Detection

Leak detection can also be included in the systems previously described.Detecting leaks is important because it can lower the efficiency of thesystem. To detect a leak of air into the system, the flow rate of airand coolant back into the system should be measured. The flow rate ofcoolant may be measured by measuring the time it takes to fill one ofthe chambers (i.e., 2206, 2208) because the volume of those chambers isalready known. Placing a level sensor in the chamber (see FIG. 22, part2260) which sends a signal to the controller 2232 would allow thecontroller 2232 to calculate the coolant flow throughout the system.Alternatively, a flowmeter may be placed on the coolant line to measurethe flow directly.

The flow rate of air may be measured by a flowmeter (see FIG. 22, part2262) in the vacuum line 2202, that outputs a signal to the controller2232. This flowmeter 2262 may be, but is not limited to, a hot wire,laminar flow element, orifice, or venturi. Under normal operation, whenthe main chamber 2206 is filling under suction, there will be a periodwhen the air in the main chamber 2206 is being pumped down to thecorrect negative pressure level. After that period the negative pressurelevel will stabilize, and the flow rate of air should be equal to theflow rate of coolant. As is known in the art, air may dissolve in wateror other coolants, and the maximum amount that can be dissolved as afunction of temperature and pressure is well known. For example at 80 F,up to 1.6% air may be present in water. Therefore, if an air leakexists, it may be detected by measuring the air flow rate out of a pumpchamber (i.e., 2206, 2208), comparing it to the coolant flow rate intothe pump chamber, and if the air flow rate is excessive this wouldindicate an air leak and an alarm would optionally be activated to alertthe operator that a leak is present. This comparison and triggering ofthe alert may be performed by the controller 2232.

For example, if the vacuum pump has a displacement of 0.05 liters perrevolution, and it spins at 1500 RPM, then it should flow 75 liters perminute. There are some losses and leaks within the vacuum pump, but theyare repeatable and known for a given pump. Therefore given the RPM ofthe pump, and the pressure at the inlet, then the mass flow rate can bedetermined using the ideal gas law. The flow rate can also be measuredat the vacuum pump outlet by means of a thermal mass flowmeter, or aventuri, orifice or other flow meter. The flow meter should becalibrated for humid air. The temperature and pressure of the waterentering and leaving the cooling system is known, and this can be usedto predict the amount of air that is dissolved in the water. It can alsobe used to predict the amount of water vapor in the gas above the water.The maximum amount of air that can be evolved from the water is thedifference between the amount that could be dissolved at the temperatureand pressure of the water leaving the cooling system, and the amount ofair that could be in the water returning to the system. The controllercould use a look up table to calculate the two amounts and thedifference that would be expected at the system air outlet. If theamount of air in the water returning to the pump from the servers isexcessive, then an alarm could activated. A humidity sensor could beused to determine how much of the gas evolved is water vapor, or testingcould be used to determine the range of outlet humidity. For example, ina typical system with a single vacuum pump the maximum vacuum achievedwith no air leaks and a flow of 1 gal/min of water might be 24 in Hg. Ifthere is a leak of 0.03 ft³/min of air into the system then the maximumvacuum will be only 20 in Hg, and this would indicate a leak or a vacuumpump failure.

The invention has been described in connection with specific embodimentsthat illustrate examples of the invention but do not limit its scope.Various example systems have been shown and described having variousaspects and elements. Unless indicated otherwise, any feature, aspect orelement of any of these systems may be removed from, added to, combinedwith or modified by any other feature, aspect or element of any of thesystems. As will be apparent to persons skilled in the art,modifications and adaptations to the above-described systems and methodscan be made without departing from the spirit and scope of theinvention, which is defined only by the following claims. Moreover, theapplicant expressly does not intend that the following claims “and theembodiments in the specification to be strictly coextensive.” Phillipsv. AHW Corp., 415 F.3d 1303, 1323 (Fed. Cir. 2005) (en banc).

The invention claimed is:
 1. A system for cooling at least oneelectrical device, comprising: a pump connected to a vacuum line, thepump creating a pressure of less than atmospheric on the vacuum line; avalve assembly connected to a pressurized line and the vacuum line; acoolant circuit that allows coolant to circulate through a first coolantchamber, a second coolant chamber, a primary heat exchanger and aelectrical device heat exchanger, wherein the first coolant chamber andthe second coolant chamber are connected to the valve assembly; and acontroller adapted to operate the valve assembly so as to propel thecoolant through the coolant circuit at below atmospheric pressure; andwherein said controller is configured to alternate the system between atleast a first mode and a second mode: in the first mode the controlleris configured to actuate the valve assembly to create a higher pressurein the first coolant chamber relative to the second coolant chamber, toempty coolant from the first coolant chamber and to draw coolant intothe second coolant chamber; and in the second mode the controller isconfigured to actuate the valve assembly to create a higher pressure inthe second coolant chamber relative to the first coolant chamber, toempty coolant from the second coolant chamber and to draw coolant intothe first coolant chamber.
 2. The system of claim 1, further comprisinga reservoir connected to the coolant circuit.
 3. The system of claim 2,wherein the reservoir comprises a coolant level sensor, and the sensoris connected to the controller.
 4. The system of claim 1, wherein theprimary heat exchanger is a liquid/liquid heat exchanger.
 5. The systemof claim 1, wherein the pressurized line is at a higher pressure thanthe vacuum line.
 6. The system of claim 1, wherein the vacuum lineand/or the pressurized line are connected to a coolant recovery device.7. The system of claim 6, wherein the coolant recovery device isselected from a group consisting of: a muffler, an air/water separatorand a thermoelectric device.
 8. The system of claim 6, wherein thecoolant recovery device is connected to one or both of the coolantchambers, such that recovered coolant is drawn back into the chambers.9. The system of claim 1, further comprising: a supply side valve inproximity to the electrical device heat exchanger, the supply side valveconnected to the circuit; wherein the coolant travels through thecircuit in a circuit direction, the circuit direction is from the supplyside valve to the electrical device heat exchanger; and wherein thesupply side valve allows coolant to flow substantially in the circuitdirection and allows a slight air leak to flow in a direction oppositeto the circuit direction.
 10. The system of claim 9 wherein the supplyside valve is selected from a group consisting of: a check valve, afluid diode, or a poppet.
 11. The system of claim 1, wherein both thefirst coolant chamber and the second coolant chamber include a pair ofone-way valves to control the flow of coolant.
 12. The system of claim1, further comprising a temperature sensor along the circuit, thetemperature sensors connected to the controller.
 13. The system of claim1, further comprising a filter disposed of in the circuit, the filteradapted to filter debris from the coolant.
 14. The system of claim 1,further comprising a test valve and a purge valve in the circuit, thetest valve adapted to close and the purge valve to open to introduce airinto the system and evacuate coolant from the electrical device heatexchanger.
 15. The system of claim 1, further comprising a pressuresensor along the circuit, the pressure sensors connected to thecontroller.
 16. The system of claim 1 further comprising: a flow meterfor detecting an air leak; and the controller being further configuredfor triggering an alert when an air leak is detected.
 17. The system ofclaim 1, further comprising: a flowmeter on the vacuum line, theflowmeter outputting a first signal to the controller; a secondflowmeter for detecting the flowrate of the coolant and outputting asecond signal to the controller; wherein the controller detects a leakby comparing the first signal to the second signal and wherein thecontroller triggers an alert when a leak is detected.
 18. The system ofclaim 1, wherein the valve assembly further comprises a first and secondpressure valves connected to the pressurized line and a first and secondvacuum valves connected to the vacuum line; and wherein the firstcoolant chamber is connected to the first pressure valve and the firstvacuum valve and the second coolant chamber is connected to the secondpressure valve and the second vacuum valve.
 19. The system of claim 1,further comprising: a return side nozzle in proximity to the electricaldevice heat exchanger, the return side nozzle connected to the circuit;wherein the coolant travels through the circuit in a circuit direction,the circuit direction is from the electrical device heat exchanger tothe return side nozzle; and wherein the nozzle allows coolant tosubstantially flow in the circuit direction and restricts an amount ofair to flow in the circuit direction.
 20. The system of claim 19,wherein the nozzle is a venturi.